Conditional Expressions

---

	Korn Shell: Unix and Linux Programming Manual, Third Edition, The By Anatole Olczak
	Table of Contents
	Appendix G.  Pdksh Quick Reference

---

The [[...]] command is used to evaluate conditional expressions with file attributes, strings, and integers. The basic format is:

[[expression]]

where expression is the condition you are evaluating. There must be whitespace after the opening brackets, and before the closing brackets. Whitespace must also separate the expression arguments and operators. If the expression evaluates to true, then a zero exit status is returned, otherwise the expression evaluates to false and a non-zero exit status is returned.

[[...]] String Operators

n string	true if length of string is not zero
o option	true if option is set
z string	true if length of string is zero
string1 = string2	true if string1 is equal to string2
string1 != string2	true if string1 is not equal to string2
string = pattern	true if string matches pattern
string != pattern	true if string does not match pattern
string1 < string2	true if string1 is less than string2
string1 > string2	true if string1 is greater than string2

[[...]] File Operators

a file	true if file exists
b file	true if file exists and is a block special file
c file	true if file exists and is a character special file
d file	true if file exists and is a directory
f file	true if file exists is a regular file
g file	true if file exists and its setgid bit is set
G file	true if file exists and its group id matches the current effective group id
k file	true if file exists and its sticky bit is set
L file	true if file exists and is a symbolic link
O file	true if file exists and is owned by the effective user id
p file	true if file exists and is a fifo special file or a pipe
r file	true if file exists and is readable
s file	true if file exists and its size is greater than zero
S file	true if file exists and is a socket
t n	true if file descriptor n is open and associated with a terminal device
u file	true if file exists and its set user-id bit is set
w file	true if file exists and is writable
x file	true if file exists and is executable. If file is a directory, then true indicates that the directory is readable.
file1 ef file2	true if file1 and file2 exist and refer to same file
file1 nt file2	true if file1 exists and is newer than file2
file1 ot file2	true if file1 exists and is older than file2

[[...]] Integer Operators

exp1 eq exp2	true if exp1 is equal to exp2
exp1 ne exp2	true if exp1 is not equal to exp2
exp1 le exp2	true if exp1 is less than or equal to exp2
exp1 lt exp2	true if exp1 is less than exp2
exp1 ge exp2	true if exp1 is greater than or equal to exp2
exp1 gt exp2	true if exp1 is greater than exp2

---

Top